Presently, congestive heart failure is one of the leading causes of cardiovascular disease-related deaths in the world. Clinically, congestive heart failure involves circulatory congestion caused by heart disorders that are primarily characterized by abnormalities of left ventricular function and neurohormonal regulation. Congestive heart failure occurs when these abnormalities cause the heart to fail to pump blood at a rate required by the metabolizing tissues. The effects of congestive heart failure range from impairment during physical exertion to a complete failure of cardiac pumping function at any level of activity. Clinical manifestations of congestive heart failure include respiratory distress, such as shortness of breath and fatigue, and reduced exercise capacity or tolerance.
Several factors make the early diagnosis and prevention of congestive heart failure, as well as the monitoring of the progression of congestive heart failure, relatively difficult. First, the onset of congestive heart failure is generally subtle and erratic. Often, the symptoms are ignored and the patient compensates by changing his or her daily activities. As a result, many congestive heart failure conditions or deteriorations in congestive heart failure remain undiagnosed until more serious problems arise, such as pulmonary edema or cardiac arrest. Moreover, the susceptibility to suffer from congestive heart failure depends upon the patient's age, sex, physical condition, and other factors, such as diabetes, lung disease, high blood pressure, and kidney function. No one factor is dispositive. Finally, annual or even monthly checkups provide, at best, a “snapshot” of patient wellness and the incremental and subtle clinicophysiological changes which portend the onset or progression of congestive heart failure often go unnoticed, even with regular health care. Documentation of subtle improvements following therapy, that can guide and refine further evaluation and therapy, can be equally elusive.
Nevertheless, taking advantage of frequently and regularly measured physiological measures, such as recorded manually by a patient, via an external monitoring or therapeutic device, or via implantable device technologies, can provide a degree of detection and prevention heretofore unknown. For instance, patients already suffering from some form of treatable heart disease often receive an implantable pulse generator (IPG), cardiovascular or heart failure monitor, therapeutic device, or similar external wearable device, with which rhythm and structural problems of the heart can be monitored and treated. These types of devices are useful for detecting physiological changes in patient conditions through the retrieval and analysis of telemetered signals stored in an on-board, volatile memory. Typically, these devices can store more than thirty minutes of per heartbeat data recorded on a per heartbeat, binned average basis, or on a derived basis from, for example, atrial or ventricular electrical activity, minute ventilation, patient activity score, cardiac output score, mixed venous oxygen score, cardiovascular pressure measures, and the like. However the proper analysis of retrieved telemetered signals requires detailed medical subspecialty knowledge, particularly by cardiologists and cardiac electrophysiologists.
Alternatively, these telemetered signals can be remotely collected and analyzed using an automated patient care system. One such system is described in a related, commonly assigned application U.S. Pat. No. 6,312,378, issued Nov. 6, 2001, the disclosure of which is incorporated herein by reference. A medical device adapted to be implanted in an individual patient records telemetered signals that are then retrieved on a regular, periodic basis using an interrogator or similar interfacing device. The telemetered signals are downloaded via an internetwork onto a network server on a regular, e.g., daily, basis and stored as sets of collected measures in a database along with other patient care records. The information is then analyzed in an automated fashion and feedback, which includes a patient status indicator, is provided to the patient.
While such an automated system can serve as a valuable tool in providing remote patient care, an approach to systematically correlating and analyzing the raw collected telemetered signals, as well as manually collected physiological measures, through applied cardiovascular medical knowledge to accurately diagnose the onset of a particular medical condition, such as congestive heart failure, is needed. One automated patient care system directed to a patient-specific monitoring function is described in U.S. Pat. No. 5,113,869 ('869) to Nappholz et al. The '869 patent discloses an implantable, programmable electrocardiography (ECG) patient monitoring device that senses and analyzes ECG signals to detect ECG and physiological signal characteristics predictive of malignant cardiac arrhythmias. The monitoring device can communicate a warning signal to an external device when arrhythmias are predicted. However, the Nappholz device is limited to detecting tachycardias. Unlike requirements for automated congestive heart failure monitoring, the Nappholz device focuses on rudimentary ECG signals indicative of malignant cardiac tachycardias, an already well established technique that can be readily used with on-board signal detection techniques. Also, the Nappholz device is patient specific only and is unable to automatically take into consideration a broader patient or peer group history for reference to detect and consider the progression or improvement of cardiovascular disease. Moreover, the Nappholz device has a limited capability to automatically self-reference multiple data points in time and cannot detect disease regression even in the individual patient. Also, the Nappholz device must be implanted and cannot function as an external monitor. Finally, the Nappholz device is incapable of tracking the cardiovascular and cardiopulmonary consequences of any rhythm disorder.
Consequently, there is a need for a systematic approach to detecting trends in regularly collected physiological data indicative of the onset, progression, regression, or status quo of congestive heart failure diagnosed and monitored using an automated, remote patient care system. The physiological data could be telemetered signals data recorded either by an external or an implantable medical device or, alternatively, individual measures collected through manual means. Preferably, such an approach would be capable of diagnosing both acute and chronic congestive heart failure conditions, as well as the symptoms of other cardiovascular diseases. In addition, findings from individual, peer group, and general population patient care records could be integrated into continuous, on-going monitoring and analysis.